Boating advice: Stopping corrosion (Part 1)

Who would have thought a minor bingle with a wharf, bending a pulpit (bow rail) on a common production yacht would cause a sail drive unit to fail four hours later?

A transom shield on another well-known production cruiser basically disintegrates six months after being slipped, and causes the engines to become a total loss from submersion.

A propeller throws a blade at 25 knots, 40 miles from land.

An aerial cable inside a mast has its outer sheath worn, and causes major issues with a keel. All of these have one thing in common, and are all linked to the C-word – Corrosion.

In years gone by, the majority of vessels were simple, they had basic electrical systems, metal fittings were limited to the skin fittings, shafts, propellers, skegs and some boarding platform struts, and on yachts the big heavy item known as keel.

As the industry has evolved and technology has played a bigger role in boating, we all want the latest gadgets; we no longer want to trim our sails manually, we want to press a button; boarding platforms no longer have a swim ladder to aid getting out of the water, they lower into the water.

Bow and Stern thrusters are a must for the modern boatie as the skill of mastering a vessel dies off.

There has been a shift in design from shaft-driven boats to cruisers with legs or pods and more and more yachts are now fitted with saildrive units.

Now let’s throw in the berthing situation at your local marina, no longer is the average boat driving a battery charger to be ready to go for the next outing or keeping the hot water warm for that instant shower after a swim. We now have all the creature comforts of home like air-conditioning, washing machines, dishwashers… the list goes on.

All of these devices draw huge loads of power from the shore to your boat sitting in water, or from the on-board power station known as the generator,  and we also have invertors, convertors and on and on.

From early in our lives we learnt that electricity and water don’t mix, and one area that has been left behind all this technology is the remedy to the causes of corrosion on boats.

Thankfully, many Australian-built boats are well up to date on practices and lead the way over the imports from the U.S. and Europe.

Over the years, I have seen all the common issues associated with stern drives, propellers, seacocks, fittings and a lot more items that can suffer corrosion. The main solution has been that if we keep the anodes up, this will save the day. Wrong.

Firstly let’s get a little technical on the meanings:
Rust
Rust is of very low ferocity compared to electrolysis corrosion. It can only be present when there is moisture in the air. Rust is easily prevented or maintained by a good protective coating like paint.

Galvanic corrosion
Compared to electrolysis corrosion, galvanic corrosion is also of low ferocity. Galvanic corrosion is caused by the natural voltage between two different metals in a conductor such as fresh and salt water. The voltage is low and not much north of 1v and the current is in the millionths of an amp. Galvanic Corrosion is at a very low level compared to electrolysis. Sacrificial anodes are used to combat this low range effect. But as we go further on in this series, you will find the humble zinc anode has had a makeover of sorts and an Australian company is leading the way.

Electrolysis
Electrolysis is at the other range of corrosion ferocity scale compared to rust and galvanic corrosion. We are talking one thousand to one million times more active. It is generated through the motor, plumbing, propeller, keel, metal hull and all fittings having a voltage different to the earth or any other source. It flows as current from an installation to the earth or other vessels and installations. Creating a full circuit, basically the outgoing current isn’t the issue, problems occur when it can get back in. This is where we need the corrosion specialist and the cause needs to be identified. More often than not, the solution is relatively easy and common, like no isolation switches to the engine or there being no electrolysis blocker installed.

Over the years corrosion is an area that has worried me deeply. The cases of gear failure and vessel submersions from corrosion-affected parts are on the rise dramatically. In looking into this further, I was fortunate enough to strike a great professional relationship with Brian Gatt an expert in the field from Logix Group.

In coming articles we are going to get into the specifics of corrosion issues on a variety of differently constructed vessels; what to look for, what you need to do to fix the problem and preventive measures that should go into every boat owner’s diary.

Education is the only way we will combat this issue in our industry. If we choose to ignore it, we will have to pay a price one day. So stay tuned as we try to work our way through the issue of corrosion in the coming weeks.

*Gavin Clark is a contributor at boatsales.com.au and BoatPoint.com.au who writes under the pseudonym 'The Surveyor'. He is a shipwright and marine surveyor with a business called Slipstream Marine based in Sydney. He has 27 years experience in the boating industry, is an avid boater and owner of a 33ft Sharpie (trawler). Gavin can be contacted at http://boatsurveying.com.au